Essentially every commercial building having more than one floor is equipped with a commercial elevator system. High-rise buildings have fast cable lifted elevators that are very complicated and expensive due to the necessary controls and safety features. In low-rise buildings, hydraulic elevators are often used and are normally very slow.
Commercial units are designed to serve multiple floors by simply adding necessary electronics and mechanical components to allow the desired number of stops. These designs must be able to locate each floor and stop precisely at the same point independent of the load being carried. They must also travel relatively slowly in order to minimize the jolting sensation at start and stop. Although some designs allow for a ‘soft’ start (the electric motor power is ramped up and down at start and stop), the travel rate must still be relatively slow for safety reasons. The electronics required to locate each floor are costly as are the mechanical brakes necessary to hold the car on each floor.
Elevators available for personal residences are typically scaled down versions of commercial elevators. By replicating the design of smaller commercial units, residential elevators retain those units inherent inefficiency when applied to a two-stop application. They are typically expensive and slow.
A need has been recognized for a simplified elevator system for the typical two-story residence. For example, U.S. Pat. No. 5,152,374 discloses an elevator system for a two-story building having two carriages mounted in a counterbalanced arrangement and both supported and moved by a pair of chains driven by a sprocket system. This arrangement shares many of the characteristics of commercial cable and drum lifted elevators including the need for controls to stop the carriages at the two floor levels, a braking system and safety features to allow a person to release doors in event of failure of the system.